1. Field of the Invention
The present invention generally relates to the extraction of various components from mineral ores. More particularly, it relates to the separation of the components of laterites into commercially valuable materials.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Laterites are soil types rich in iron and aluminum, formed in hot and wet tropical areas. Nearly all laterites are rust-red in color due to the presence of iron oxides. They develop by intensive and long-lasting weathering of the underlying parent rock. Tropical weathering (laterization) is a prolonged process of chemical weathering which produces a wide variety in the thickness, grade, chemistry and ore mineralogy of the resulting soils. The majority of the land area containing laterites is located in a band extending about 25 degrees north and south of the Equator.
Historically, laterite was cut into brick-like shapes and used in monument building. Since the mid-1970's, trial sections of bituminous-surfaced low-volume roads have used laterite in place of stone as a base course. Thick laterite layers are porous and slightly permeable and thus the layers may function as aquifers in rural areas. Locally available laterites are used in an acid solution, followed by precipitation to remove phosphorus and heavy metals at sewage treatment facilities.
Laterites are a source of aluminum ore. The ore exists largely in clay minerals and the hydroxides, gibbsite, boehmite, and diaspore, which resembles the composition of bauxite. In Northern Ireland, they once provided a major source of iron and aluminum ores. Laterite ores also were the early major source of nickel.
Iron contamination can be a problem with regard to alumina recovery through acid digestion of alumina-rich earths or laterites. Crystallization routes almost always result in iron inclusions.
In a process according to the present invention, iron conversion to the ferrous form minimizes iron inclusions. Additionally, conversion of all iron to the ferrous form allows iron separation by precipitation as an oxalate.
Separation may be complete and the iron chemically pure. Multiple crystallizations from an ammonium alum avoid caking and other problems occurring when simple ammonium sulfate is crystallized and calcined. During development of the invention, the principal challenges were chemistry-related in terms of testing the reactions and finding the correct range of chemicals, temperatures, pH etc. to make the process work.
In the past, laterite separations have not been of much interest as a process for obtaining alumina. The usual approach has been to search for pure alumina feeds where possible, with minimal iron as a contaminant.
Thus, bauxite feeds have been dissolved in caustic soda (the Bayer process) rejecting all iron as the hydroxide (red mud). In a process according to the present invention, value may be derived from all of the constituents of laterite.